String.IsNullOrEmpty Method (String)
Indicates whether the specified string is null or an Empty string.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- value
-
Type:
System.String
The string to test.
Return Value
Type: System.Booleantrue if the value parameter is null or an empty string (""); otherwise, false.
IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is null or its value is Empty. It is equivalent to the following code:
You can use the IsNullOrWhiteSpace method to test whether a string is null, its value is String.Empty, or it consists only of white-space characters.
A string is null if it has not been assigned a value (in C++ and Visual Basic) or if has explicitly been assigned a value of null. Although the composite formatting feature can gracefully handle a null string, as the following example shows, attempting to call one if its members throws a NullReferenceException.
Module Example Public Sub Main() Dim s As String Console.WriteLine("The value of the string is '{0}'", s) Try Console.WriteLine("String length is {0}", s.Length) Catch e As NullReferenceException Console.WriteLine(e.Message) End Try End Sub End Module ' The example displays the following output: ' The value of the string is '' ' Object reference not set to an instance of an object.
A string is empty if it is explicitly assigned an empty string ("") or String.Empty. An empty string has a Length of 0. The following example creates an empty string and displays its value and its length.
The following example examines three strings and determines whether each string has a value, is an empty string, or is null.
Class Sample Public Shared Sub Main() Dim s1 As String = "abcd" Dim s2 As String = "" Dim s3 As String = Nothing Console.WriteLine("String s1 {0}.", Test(s1)) Console.WriteLine("String s2 {0}.", Test(s2)) Console.WriteLine("String s3 {0}.", Test(s3)) End Sub Public Shared Function Test(s As String) As String If String.IsNullOrEmpty(s) Then Return "is null or empty" Else Return String.Format("(""{0}"") is neither null nor empty", s) End If End Function End Class ' The example displays the following output: ' String s1 ("abcd") is neither null nor empty. ' String s2 is null or empty. ' String s3 is null or empty.
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1